1. Field of the invention
The present invention relates to performing manufacturing and production line tests on a wire harness, and, more particularly, to performing a dielectric voltage-withstand test on a wire harness.
2. Description of the Related Art
It is known to perform tests on wiring harnesses after their manufacture in order to ensure the continuity and integrity of the wiring harnesses. PLC harness testers perform two primary functions; namely, verifying the continuity of each of the wires, and verifying the integrity of the insulation surrounding the wires. In order to verify the integrity of the insulation and ensure that no short circuits exist between the wires of the wire harness, an insulation dielectric voltage-withstand test is performed. More particularly, the testers perform the manufacturing and production line tests outlined by the testing requirements specified by Underwriters Laboratory for office furnishings, i.e., UL 1286.
The Dielectric Voltage-Withstand Test outlined in UL 1286 calls for a 40-70 Hz potential of 1200V to be applied to each wire of the wire harness for a duration of one second to determine whether an insulation breakdown has occurred. In essence, this test verifies the insulation integrity of all current-carrying conductors with respect to all other conductors including ground.
For the dielectric voltage-withstand test, the ground conductor does not have the dielectric voltage applied directly to it. This is because the ground conductor is connected to bare metal of the completed harness. With this, the total test time in terms of dielectric voltage-withstand is one second per conductor. Accounting for high-voltage control relay transitions, a typical eight-wire harness takes just under eight seconds to undergo the dielectric test.
What is verified during the eight-second dielectric test is that no conductor leaks any current to any other conductor or to bare metal of the harness assembly. The test sequence is as shown in FIG. 1. In the first test, voltage is applied only to wire 1. After this first test, voltage is then individually applied to each of wires 2-7 in sequence, as indicated by the second through seventh tests.
With this topology, the ground conductor connected to the bare metal is connected as wire number eight and will therefore never have the dielectric high-voltage applied to it directly as the live conductor of the high voltage potential. If any conductor hipots, i.e., short-circuits, to either bare metal or any other conductor, the hipot indicates a dielectric breakdown failure due to exceeding the current limit set by the dielectric high-voltage source.
Since voltage is applied to each of the seven conductors individually for at least one second, the total test time for a wire harness is in excess of seven seconds. This limits how quickly the wire harnesses can be tested.
What is needed in the art is a method of performing a dielectric voltage-withstand test on a wire harnesses that takes less time than known methods.
The present invention provides a method of shortening the time of a dielectric voltage-withstand test by testing multiple conductors simultaneously.
The method of the present invention reduces the number of discrete tests within the dielectric test regime from seven to three. This reduces the period of one dielectric test cycle from just below eight seconds to just over three seconds. This reduction is achieved by simultaneously applying the dielectric high-voltage to more than one conductor.
The invention comprises, in one form thereof, a method of performing a dielectric voltage-withstand test on a wire harness having a plurality of conductors. Voltage is simultaneously applied to a first subset of the conductors. The first subset includes at least two of the conductors. An electrical characteristic of each of the conductors excluded from the first subset of conductors is measured. The applying and measuring steps are repeated for at least one additional subset of the conductors. It is decided whether the wire harness passes the test based upon at least one of the measuring steps.
An advantage of the present invention is that less time is required to perform a dielectric voltage-withstand test on a wire harness.
Another advantage is that the method of the present invention is more sensitive to the actual monitored leakage current between the conductors of the wire harness.